Thoughts on Soil Filter Gradation Design

Three papers published in the 1980s (Sherard et al, 1984a, 1984b; and Sherard & Dunnigan, 1989) presented the results of Natural Resources Conservation Service (NRCS)1 research on soil filters. Between the mid-1980s and the mid-1990s, the NRCS; the US Department of the Interior, Bureau of Reclamation (Reclamation); and the US Army Corp of Engineers (USACE) incorporated the results of that research into published guidelines on soil filter gradation design. These guidelines, and their subsequent updates, now represent the state of the practice for soil filter gradation design.

The research and the resulting guidelines were a substantial advancement in soil filter design. All of the noted agency guidelines and a subsequently published Federal Emergency Management Agency (FEMA) document (FEMA, 2011) present step-by-step procedures for establishing limits for soil filter gradations. Some agencies, organizations, and practitioners have incorporated the step-by-step guidance into spreadsheet applications to facilitate calculations. One clear advantage to the step-by-step guidelines is consistency in filter gradation design calculations among different practitioners. (Continued)